Thank you for posting your issue on Microsoft Q&A.
I understand that you are not receiving authenticator code when trying to sign in azure portal.
Microsoft authenticator code will be sent to old phone. To get authenticator code in new phone you should need to register account in new phone.
Contact your global administrator to Re-register MFA. Follow the below steps:
1.Sign in to the Microsoft Entra admin center
2.Click on “Users” in the Microsoft Entra ID pane > Select the user.
3.In the user profile pane, select Authentication methods”.
4.Look for the option “Require re-register MFA.”
For more information: https://zcusa.951200.xyz/en-us/entra/identity/authentication/howto-mfa-userdevicesettings#manage-user-authentication-options
When you sign in again, user will be prompted to set up your MFA. Follow the prompts to add the Microsoft Authenticator app again in your new phone and sign in account you will receive code.
Hope this helps. Do let us know if you have any further queries.
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Thanks,
B. Siri Chandana.